July 2nd
Day 72

RainWater (RWH) Tank:

Last blog talked about center-marking pillars.. You would notice in this video a number of such pillars are now set up to mark various edges. Also, various rooms are now filled with sand (aka earth material). Once foundation masonry layers are completed they will start consolidating earth material in each of the rooms. This process is equivalent to making dough. The volume of dough shrinks as it absorbs water.. Similarly, they alternate process of adding earth material and water so that rooms themselves are flush with dense earth material. The idea behind this is - more dense the earth material, less chances of air bubbles within that and therefore less chances of house settling in ground. 

Best way to describe RWH tank is through pictures that describe various phases. As a reminder, tank has a capacity of about 60,000 litres. For more description on how I arrived at 60,000, refer to <>. Tank area was excavated about 7' below the natural ground level. Further, tank is built-up to be about 2.5' above ground level - in line with the plinth beam.

Next step is to to setup steel re-inforcements to provide structural support. At the base of the tank, they criss-cross steel rods and tie them together with hooks. Then, vertical rods are tied at the edge with the flooring. Finally, similar criss-cross pattern is setup at the walls of the RWH tank. It is important to excavate tank about 1' wider than the required capacity so as to allow workers to perform their work. Although the structure looks a bit daunting actual work didn't take more than 6-7 days.

Once steel structure is established, pouring concrete on the floor is fairly straightforward. Doing the walls is more complicated though. Essentially, they split-up wall into 3-layers, each 2.5' tall. Then, across the boundary of RWH tank, both sides of vertical steel rods are "bound" with wooden planks. As the picture shows, wooden planks themselves are supported with wooden rods. Finally, concrete is poured in to them. All said and done, each layer takes about 4 days, and it took about 12 days to get the tank done.

Final step involves a few minor, but important activities

1. Sloping at the floor pointing towards the manhole. The intent being while cleaning the tank all water should accumulate near the manhole. 
2. Water the concrete to allow it to strengthen. Plaster the walls and floor for nice and consistent finish.
3. Apply chemical treatment on walls to make them water proof. Test for leakages by spraying water and checking for dampness on the outside.
4. Fill the outside of RWH tank with earth material. Allow them to consolidate to form completely immersed structure. 

All said and done, it took about 30 days to complete this tank. Besides cost, this delayed the project a bit.. I am hopeful though this investment will some day prove worth it.

Completed tank:

Next post will cover plinth beam casting.